The typical optical scanner devices, such as well-known flat bed scanners, produce machine-readable image data from an original. The original could be a document, a photograph, or a transparency. For further computer applications, many users often transform the retrieved image data into a digital format and then output them to proper devices, such as monitors or printers. When the image data are transferred to a computer, users could edit, copy, and save them in accordance with their own preferences.
To meet needs for further image processing, it is desirable for users to adjust a resolution of a scanner. The resolution of the scanner means the number of pixels per unit length of the image data scanned from an original. If a coarse representation of the original can be accepted, users may reduce the amount of the scanned image data by selecting a low resolution. On the contrary, if a fine representation of the original is required for some applications, selecting a low resolution will not fulfill the quality requirement of applications Therefore, if users need a delicate image, a high resolution resulting in a large number of digital data is needed.
However, the resolution of the scanner usually is limited by the precision of an optical device, which could be influenced by manufacture techniques of a charge coupled device (CCD) or a contact image sensor (CIS) in the optical device.
As for current scanners, high resolution optical scanners have been proposed which are generally of a high cost due to the electro-optic transducers, known as CCDs, required for high resolution.
Alternatively, the effective resolution may be increased over the native resolution by using various data interpolation techniques For example, some data interpolation techniques can be used to increase the effective resolution to 600 or even 1200 dpi with a charge coupled device (CCD) having a native resolutions of only 300 dpi.
While the techniques described above are useful in increasing the effective resolution, they accompany disadvantages. For example, the interpolation techniques used to increase the resolution may require a substantial amount of processor time and/or memory, requiring more time to perform the scan operation. Or, it requires a faster processor and/or more memory if higher resolution is to be achieved without adversely affecting the overall scan time.
FIG. 1 shows a schematic diagram of a scanning apparatus for scanning a reflective original according to the prior art The scanning apparatus of the prior art includes a light source 11 and a scanning module 13
As shown in FIG. 1, an original 10 is placed on an image plane 12 of a scanning module 13. The original 10 is a reflective document. The light source 11 illuminates the original 10 and produces an image. The image is projected to the scanning module 13. The scanning module 13 receives the image to process the scanning. Here, the resolution of the image depends on the scanning module 13 If the resolution of scanning module 13 is high, a high quality image is obtained. However, if the resolution of scanning module 13 is low, instead, a coarse image with a restricted resolution is obtained.
FIG. 2 shows a schematic diagram of a scanning apparatus for scanning a transparent original according to the prior art. The scanning apparatus of the prior art includes a light source 21 and a scanning module 13.
As shown in FIG. 2, an original 20 is placed on an image plane 12 of a scanning module 13. The original 20 is a transparent document. The light source 21 illuminates the original 20 and produces an image. The image is projected to the scanning module 13. The scanning module 13 receives and processes the scanning. Here, the resolution of the image also depends on the scanning module 13
Additionally, in the scanning apparatus of the prior art, the original is placed on the image plane 12. Thus, the scanning apparatus precisely focuses on the surface of glass platform of the image plane 12. However, the positive original usually has a noticeable thickness. Therefore, when scanning the positive original, the obtained image will not be sharp due to out-of-focus resulting from unexpected thickness.
As a result, a scanning apparatus not limited by resolution of scanning module is desired. Besides, it is also important to avoid out-of-focus issue mentioned above.